Aircraft On-Board Oxygen Generation Systems/On-Board Inert Gas Generation Systems (OBOGS/OBIGGS) units are designed to separate gases from a pressurized air source in order to supply oxygen enriched air flow to the flight crew, while also supplying oxygen depleted air flow for inerting the fuel tank ullages. Such units typically employ molecular sieve gas separation processes, such as but not limited to pressure swing adsorption (PSA), wherein molecular sieve particulate material, such as a zeolite, is packed as a bed and retained within a molecular sieve unit. The sieve unit includes a housing, an inlet end cap, an outlet end cap and the sieve bed packed therein. A pressurized inlet gas may then enter through the inlet end cap, pass through the sieve bed wherein the inlet gas is separated by virtue of the sieve material such that unwanted components of the inlet air (e.g., N2) are selectively adsorbed by the sieve material while a desired product gas (e.g., O2) may pass through the sieve material and exit through the outlet end cap.
To prevent unwanted movement of the particulate material of the sieve bed within the housing, traditional sieve housings include a plate and spring retention system where the spring provides a downward force upon the plate to maintain a compact bed. Such a force acts to inhibit the formation of gaps through which unwanted components of the inlet air may traverse the length of the housing rather than be adsorbed by the particulate material of the sieve bed. The challenge is to provide sufficient downward force upon the packed bed so that the sieve particles do not move relative to each other under severe application conditions while also avoiding force levels that crush the particles. The probability of achieving this condition is increased dramatically when the compaction force applied to the sieve bed is uniform across the cross sectional area that it is applied. With that in mind, previous sieve beds have utilized conical springs coupled to a perforated plate to provide the compaction force to spread the load to the packed bed. However, under extreme environmental conditions, the packed bed and its retention system may be subject to forces that can cause rocking and or tilting of the perforated plate, which can in turn result in movement of the packed bed and subsequent damage to the molecular sieve unit. The risk of this type of failure increases if there is even a slight misalignment of the perforated plate or spring during assembly.
Therefore, a need remains for a molecular sieve retention system which can withstand the forces experienced due to extreme environmental conditions without risk of material bed damage and/or loss of sieve material retention.